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[PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer

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  [PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer Gustavo Padovan <gustavo@padovan.org> - 2016-02-02 14:30 +0100
    Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64  pointer Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-02-02 15:20 +0100
      Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64  pointer Gustavo Padovan <gustavo@padovan.org> - 2016-02-02 21:30 +0100
        Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64  pointer Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-02-03 09:40 +0100
    Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer Emil Velikov <emil.l.velikov@gmail.com> - 2016-02-02 16:30 +0100

#1324076 — [PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Making fence_info a pointer enables us to extend the struct in the future
without breaking the ABI.

v2: use type __u64 for fence_info

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/staging/android/sync.c      | 2 +-
 drivers/staging/android/uapi/sync.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index f7530f0..03b1214 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (info->status >= 0)
 		info->status = !info->status;
 
-	len = sizeof(struct sync_file_info);
+	len = sizeof(struct sync_file_info) - sizeof(__u64);
 
 	for (i = 0; i < sync_file->num_fences; ++i) {
 		struct fence *fence = sync_file->cbs[i].fence;
diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
index ed281fc..8e2ed32 100644
--- a/drivers/staging/android/uapi/sync.h
+++ b/drivers/staging/android/uapi/sync.h
@@ -54,7 +54,7 @@ struct sync_file_info {
 	char	name[32];
 	__s32	status;
 
-	__u8	fence_info[0];
+	__u64	fence_info;
 };
 
 #define SYNC_IOC_MAGIC		'>'
-- 
2.5.0

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#1324117 — Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer

Op 02-02-16 om 14:23 schreef Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>
> Making fence_info a pointer enables us to extend the struct in the future
> without breaking the ABI.
>
> v2: use type __u64 for fence_info
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
>  drivers/staging/android/sync.c      | 2 +-
>  drivers/staging/android/uapi/sync.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> index f7530f0..03b1214 100644
> --- a/drivers/staging/android/sync.c
> +++ b/drivers/staging/android/sync.c
> @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>  	if (info->status >= 0)
>  		info->status = !info->status;
>  
> -	len = sizeof(struct sync_file_info);
> +	len = sizeof(struct sync_file_info) - sizeof(__u64);
>  
>  	for (i = 0; i < sync_file->num_fences; ++i) {
>  		struct fence *fence = sync_file->cbs[i].fence;
> diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
> index ed281fc..8e2ed32 100644
> --- a/drivers/staging/android/uapi/sync.h
> +++ b/drivers/staging/android/uapi/sync.h
> @@ -54,7 +54,7 @@ struct sync_file_info {
>  	char	name[32];
>  	__s32	status;
>  
> -	__u8	fence_info[0];
> +	__u64	fence_info;
>
With the information from the commit I would expect fence_info would be a true pointer.

so if (sync_file_info->num_fences == 0) not copying fence_info, but set all members including this one.
else for_all_fences() copy_to_user(fence_info struct)

Otherwise you still can't extend the struct without breaking the abi.

~Maarten

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#1324596 — Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer

Hi Maarten,

2016-02-02 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>:

> Op 02-02-16 om 14:23 schreef Gustavo Padovan:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> >
> > Making fence_info a pointer enables us to extend the struct in the future
> > without breaking the ABI.
> >
> > v2: use type __u64 for fence_info
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > ---
> >  drivers/staging/android/sync.c      | 2 +-
> >  drivers/staging/android/uapi/sync.h | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> > index f7530f0..03b1214 100644
> > --- a/drivers/staging/android/sync.c
> > +++ b/drivers/staging/android/sync.c
> > @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> >  	if (info->status >= 0)
> >  		info->status = !info->status;
> >  
> > -	len = sizeof(struct sync_file_info);
> > +	len = sizeof(struct sync_file_info) - sizeof(__u64);
> >  
> >  	for (i = 0; i < sync_file->num_fences; ++i) {
> >  		struct fence *fence = sync_file->cbs[i].fence;
> > diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
> > index ed281fc..8e2ed32 100644
> > --- a/drivers/staging/android/uapi/sync.h
> > +++ b/drivers/staging/android/uapi/sync.h
> > @@ -54,7 +54,7 @@ struct sync_file_info {
> >  	char	name[32];
> >  	__s32	status;
> >  
> > -	__u8	fence_info[0];
> > +	__u64	fence_info;
> >
> With the information from the commit I would expect fence_info would be a true pointer.

I missed that. It is fixed for v3 now.

> 
> so if (sync_file_info->num_fences == 0) not copying fence_info, but set all members including this one.
> else for_all_fences() copy_to_user(fence_info struct)
>
> Otherwise you still can't extend the struct without breaking the abi.

all sync_files have at least 1 fence so we are left to the else case,
coupy all fences to the user. So we always have variable length at the
end of the struct. But I still don't see how this will prevent us from
breaking the API.

	Gustavo

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#1325040 — Re: [PATCH v2 06/11] staging/android: turn fence_info into a __u64 pointer

Op 02-02-16 om 21:28 schreef Gustavo Padovan:
> Hi Maarten,
>
> 2016-02-02 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>:
>
>> Op 02-02-16 om 14:23 schreef Gustavo Padovan:
>>> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>>>
>>> Making fence_info a pointer enables us to extend the struct in the future
>>> without breaking the ABI.
>>>
>>> v2: use type __u64 for fence_info
>>> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>>> ---
>>>  drivers/staging/android/sync.c      | 2 +-
>>>  drivers/staging/android/uapi/sync.h | 2 +-
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
>>> index f7530f0..03b1214 100644
>>> --- a/drivers/staging/android/sync.c
>>> +++ b/drivers/staging/android/sync.c
>>> @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>>>  	if (info->status >= 0)
>>>  		info->status = !info->status;
>>>  
>>> -	len = sizeof(struct sync_file_info);
>>> +	len = sizeof(struct sync_file_info) - sizeof(__u64);
>>>  
>>>  	for (i = 0; i < sync_file->num_fences; ++i) {
>>>  		struct fence *fence = sync_file->cbs[i].fence;
>>> diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
>>> index ed281fc..8e2ed32 100644
>>> --- a/drivers/staging/android/uapi/sync.h
>>> +++ b/drivers/staging/android/uapi/sync.h
>>> @@ -54,7 +54,7 @@ struct sync_file_info {
>>>  	char	name[32];
>>>  	__s32	status;
>>>  
>>> -	__u8	fence_info[0];
>>> +	__u64	fence_info;
>>>
>> With the information from the commit I would expect fence_info would be a true pointer.
> I missed that. It is fixed for v3 now.
>
>> so if (sync_file_info->num_fences == 0) not copying fence_info, but set all members including this one.
>> else for_all_fences() copy_to_user(fence_info struct)
>>
>> Otherwise you still can't extend the struct without breaking the abi.
> all sync_files have at least 1 fence so we are left to the else case,
> coupy all fences to the user. So we always have variable length at the
> end of the struct. But I still don't see how this will prevent us from
> breaking the API.
Ok this was with fence_info not being a pointer. :)

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#1324196

On 2 February 2016 at 15:23, Gustavo Padovan <gustavo@padovan.org> wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>
> Making fence_info a pointer enables us to extend the struct in the future
> without breaking the ABI.
>
> v2: use type __u64 for fence_info
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
>  drivers/staging/android/sync.c      | 2 +-
>  drivers/staging/android/uapi/sync.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> index f7530f0..03b1214 100644
> --- a/drivers/staging/android/sync.c
> +++ b/drivers/staging/android/sync.c
> @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>         if (info->status >= 0)
>                 info->status = !info->status;
>
> -       len = sizeof(struct sync_file_info);
> +       len = sizeof(struct sync_file_info) - sizeof(__u64);
>
>         for (i = 0; i < sync_file->num_fences; ++i) {
>                 struct fence *fence = sync_file->cbs[i].fence;
> diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
> index ed281fc..8e2ed32 100644
> --- a/drivers/staging/android/uapi/sync.h
> +++ b/drivers/staging/android/uapi/sync.h
> @@ -54,7 +54,7 @@ struct sync_file_info {
>         char    name[32];
>         __s32   status;
>
> -       __u8    fence_info[0];
> +       __u64   fence_info;
Please update the description in the commit block at the top. As-is
things are very confusing :-)

-Emil

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